LensCalc

Projector Throw Distance Calculator

Where should the projector sit?

Throw Ratio

Screen Diagonal (in)

Throw Distance

3.32 m

Assumes a 16:9 screen.

Screen Width: 2.21 m
Screen Height: 1.25 m

What you entered

Throw Ratio: 1.5Screen Diagonal (in): 100

1
Screen diagonal in metres
100 in x 0.0254= 2.54 m
2
Screen width for a 16:9 screen
2.54 x 16/sqrt(16^2+9^2)= 2.2138 m
3
Throw distance
1.5 x 2.2138= 3.3207 m

Result

Throw Distance: 3.32 m

Projector throw distance for a 16:9 screen

Throw distance is the throw ratio multiplied by the screen width. The ratio is printed in the projector's specification.

Throw ratio	Screen diagonal	Screen width	Screen height	Distance needed
0.8 (short throw)	100 in	2.21 m	1.25 m	1.77 m
1.2	100 in	2.21 m	1.25 m	2.66 m
1.5 (standard)	80 in	1.77 m	1.00 m	2.66 m
1.5 (standard)	100 in	2.21 m	1.25 m	3.32 m
1.5 (standard)	120 in	2.66 m	1.49 m	3.98 m
2.0 (long throw)	100 in	2.21 m	1.25 m	4.43 m

Screen diagonal is quoted in inches but the width is what drives the distance, and a 16:9 screen is only about 87% as wide as its diagonal. Zoom lenses give a throw range rather than a single ratio.

Throw ratio is distance over width

A projector with a 1.5 throw ratio must sit 1.5 metres back for every metre of image width. It is defined against width, not diagonal, so you have to convert your screen's advertised diagonal into a width before the number is usable.

Short throw and ultra short throw

Ratios below 1.0 are short throw and below 0.4 ultra short throw, letting a projector fill a large screen from very close. They solve shadow and room-depth problems but demand precise placement — a few centimetres of error visibly distorts geometry.

Frequently asked questions

I want a 100-inch (2.2m wide) image and my projector has a 1.5 throw ratio — how far back?

Distance = throw ratio × width = 1.5 × 2.2m = 3.3 meters from the screen. Make sure your room is long enough, and add clearance behind the projector for ventilation.

How is the projector throw calculator different from the telescope magnification calculator?

The projector calculator works the optics in reverse — projecting an image outward to fill a screen. The telescope calculator describes collecting distant light to magnify it for your eye. Both involve focal lengths and ratios, but in opposite directions.

What if my throw ratio is a range like 1.2-1.9?

That means the projector has a zoom lens. At 1.2, it fills the screen from closer (2.64m for a 2.2m-wide image); at 1.9, from farther (4.18m). The range gives you placement flexibility — pick the distance that fits your room and zoom to fill the screen.

Can an ultra-short-throw projector work with a curved screen?

Generally no. UST projectors (ratio < 0.4) project at a steep angle from just inches away, so any curve in the screen surface causes visible distortion. They need a perfectly flat, smooth surface — standard screens or painted walls work best.